how to use compositer nodes on a render farm?
At GarageFarm.NET we support compositor nodes in Blender. they should work the same way as on your end. If you have multiple layers to render in the scene, then all of them will render and will ve combined as you set it up in the compositor.
If you wish to save different layers from the compositor for later post-production, then you can use the File Output node to export it. All the File Outputls nodes are correctly saved on our end. You can also use multi-layer EXR for your output which will have all your passes.
I encourage you to test our render farm. We offer trial credits so in this way you can check if everything works as you expected without any costs.